Cracking of hydrocarbon oils



May 5, 19,42'` P. c. K EITH, JR., ETAL 2,281,881

CRACKING OF HYDROGARBON OILS Filed Feb.I ll, 1937 2 Sheets-Sheet 1 ATTORNEY P. c. KEITH, JR., ETAL 2,281,881

CRACKING 0F HYDRocARBoN OILS l Filed Feb. ll. 1937 2 Sheets-Sheet 2 May 5, I1942.

QQ QN Patented May 5, 1942 UNITED STATES PATENT OFFlCE CRACKING 0F HYDROCARBON OILS Percival C. Keith, Jr., Peapack, N. J., and Joseph K. Roberts, Flossmoor, Ill., assignors of onehalf to Standard Oil Company, Chicago, Ill., a corporation of Indiana, and one-half to Gasoline Products Company, Inc., Jersey City, N. J., a corporation of Delaware Application February 11, 1937, Serial No. 125,204

9 Claims. (Cl. 196-49) This invention relates to processes for the treatment of hydrocarbon oil and pertains more particularly to processes adapted for the production of gasoline or other light distillate from heavy oil such as crude petroleum, partially reduced crude or the like.

It is an object of our invention to provide a combination cracking unit or process wherein the crude petroleum is subjected to a distillng operation to separate virgin gasoline, heavy naphtha, kerosene, gas cil and reduced crude oil, and to provide for the separate treatment of these several fractions.

A feature of our invention resides in the oncethrough cracking of the heavy reduced crude and the introduction thereof into a vapor separating and fractionating system, from which a heavy gas oil condensate is withdrawn, separately cracked, and returned to the evaporating and fractionating system, this latter operation being conducted on a recycling basis,

Another feature resides in the removal of the kerosene fraction from the process and the separate cracking or reforming of a mixture of the virgin heavy naphtha and virgin gas oil and orating and fractionating systems whereby econorny of operation is attained.

An additional feature of our invention pertains to the provision of an auxiliary furnace which is adapted for use either in cracking light to the separation thereof into its several virgin components.

In accordance with our invention the fresh heavy charging oil such as crude oil, partially reduced crude or the like, is preheated by any suitable method such as indirect heat exchange or direct heating in a red coil, or both, and then introduced into a crude flash tower, from which a gasoline fraction, heavy naphtha frac- .l

tion, kerosene fraction, gas oil fraction and reduced crude are Withdrawn. The reduced crude is passed once through a cracking heater wherein it is raised to a cracking temperature and subjected to conversion and the cracked oil is then passed to an evaporating zone, the vapors from which are subjected to fractional condensation with the resulting formation of a heavy gas oil condensate and an overhead light distillate comprising gasoline and light gas oil, C

but which may comprise substantially only gasoline. The heavy condensate is removed, passed through a separate cracking zone and returned to the evaporating zone, While the overhead light distillate is introduced into a separate rel- *atively high-pressure fractionator from which redux condensate is withdrawn, conducted through a separate cracking coil, thence to a separate high-pressure evaporator for supplying the vapors for the high-pressure fractionator. The virgin heavy naphtha and gas oil are passed together as a mixture through a third cracking zone wherein cracking and reformation take place. The products of conversion then bez ling introduced into the high-pressure evaporator.

Gasoline containing distillate from the initial low-pressure fractionator may be likewise passed through this third cracking zone for conversion into high anti-knock products if desired. The fractionated vapors from the high-pressure fractionator are removed and condensed as a desired product. y

Liquid residue from the high-pressure evaporater is preferably dashed in a ash tower un- `der reduced pressure, the flashed vapors being conducted to the low-pressure fractionating system. At the same time residue from the lowpressure evaporator is preferably withdrawn and flashed in a separate fiash drum under vacuum, the overhead distillate obtained being returned to the low-pressure 'evaporating and fractionating system, most suitably in such manner that unvaporized portions thereof are passed through the second cracking zone with the heavy conl L recycle gas oil or 1n heating the crude 011 prior de Sabe Where different types of crude oil are charged different quantities of heat must be supplied thereto for 'effecting distillation and, to accomplish this most efficiently, an auxiliary furnace is provided through which the crude charging oil may be passed in one direction prior to introduction into the crude flash tower. Provision is also made for passing recycle stock from the high-pressure fractionator in the opposite direction through this auxiliary furnace when that furnace is not being used for preheating crude oil.

The above-mentioned and further objects and advantages of our invention and the manner of attaining them will be more fully set forth in the following description taken in conjunction with the accompanying drawings.

Figure 1 illustrates diagrammatically in side elevation apparatus adapted to carry out the process of the invention.

Figure 2 is a simplified now diagram of the invention.

Referring more particularly to the drawings, heavy charging oil such as crude oil, partially reduced crude or the like is introduced through line I and forced by pump 2 into crude flash tower 3, after having passed through suitable preheating means such as heat exchangers 4 and 5. wherein the oil is raised to a distillation temperature, and by-pass line 6. Alternatively the oil may travel through heating coil 'I of furnace 8 to pick up suflicient heatfor distillation purposes, valves 9, I0, and II providing the necessary control. n

In tower 3 the crude oil is fractionally distilled to form an overhead distillate of light naphtha, i. e., the light ends of gasoline, which is removed via vapor line I2 and condenser I3 and collected in receiver I4, and naphtha, kerosene, and gas oil condensates, which are collected on trap-out trays I5, I6, and I I respectively, and reduced crude'which is collectediat the'base of the tower. These several condensates are conducted through valved lines I8, I9, and ZIJ into strippers ZI, 22 and-23 respectivelyfwherein they'are stripped of lighter4 endsr by aid of steam or gasV introduced through connections I t. The kerosene is pref erably withdrawn from the process through valvedI line 24' as a desired product while the heavy naphtha comprising heavy ends of gasoline; and gas oil condensate are introduced into accumulator 25`by wayl of valved connections 2t and 2l. The latter connection includes heat exchanger 28which may be by-passed by means of valved' line 29'. Kerosene when not withdrawn from the process'may likewise be passed to accumulator 25' through valved pipe I 5I. Vapors from the severalstrippers andfrom the accumulatorare returned to the tower 3 by means of vapor pipes'30, 3l', 32 and 33.

ReducedI crude isr withdrawn from the base of tower 3 through pipe 34 and forced by pumpr 35 through heating coil 35 located in furnace 3l, wherein it is' subjected to mild cracking conditions to4 e'iect viscosity breaking. The cracked products pass through transfer lineV 38 having control valve 31),l into the evaporator portion 4i] of combination tower 4I, wherein vapors separate from liquid residue.' The vapors travel upwardly through the tower around baffle plates or'other contact elements 42, then through fractionator section 43' ofthe tower having bubble trays or other fractionating elements' M; The fractionated vaporsA of desired'boiling characteristics', e. g., gasoline, pass through vapor pipe 45, are cooled in he'at'excharige'r- 45A and4'I, and condensed inl erate degree of conversion. The resulting cracked products pass through transfer line 56 having control valve 51 into the evaporator section 4B of tower 4I.'

Liquid residue is directed from the base of tower 4I through pipe 5B having reducing valve 59', into vacuum flash tower 60 wherein lighter constituents thereof are distilled by their con'- tained heat, leaving a heavy tar residue which is oil is raised in coil 38, and is subjected to a moddrawn olf from the process through valved line 6I having pump 62, for use alone or in mixture with other tar or distillate from the process. The vacuum flash tower may operate under an absolute pressure of, for example, about 'IU millimeters of mercury. The flashed vapors are removed through vapor pipe 63, heat exchanger 63A and condenser 64 and the distillate is collected in receiver 55, from which part is returned via line 65 under pressure of pump ISI, to the flash tower as a reiiuxing medium while the re mainder is conducted by conduit 68 into fractionator section t3 through branch connection 69 and heat exchanger 63A or through branch connections lll and 'Il into evaporator section 4U. Each of these connections is furnished with a control valve as shown. Gas oil may be circulated from tray t2 through conduit 'I2 having pump 1J3 and cooler I4 into any or all of the branch connections mentioned for use as a refluxing or cooling medium. Reference numeral lindicates an exhausting device such as a pump or barometric condenser for producing a vacuum in the flash tower.

The mixture of virgin heavy naphtha and gas oil is removed from accumulator 25 by way of pipe I5 and is forced by pump 'It through heating coil 'Il located in furnace wherein it is raised to a high cracking temperature suiicient to form high anti-knock gasoline fractions, and the crackedV products are conducted into the lower portion of evaporator I8 through pipe I9 having control valve 8c. In the evaporator vapors separate from liquid residue, thelatter being drawn off through piper 8l having reducing valve 82, into hash drum 83 wherein lighter constituents are vaporized by their contained heat leaving flashed liquid residue which is withdrawn from the process via line 84 as fuel oil. If desired this flashed residue may be blended with tar removed from vacuum flash tower El) or with bottoms from tower 81 or both. 'I'he iiashed vapors flow throughvapor pipe 85 into fractionator section IIS of tower fil.

vapors from evaporator 'I8 travel through va'- por line IlIV into fractionator 8l and are thereih fractionated in the usual way to give overhead vapors of the desired boiling characteristics, e. g., gasoline, which arey removed by way of vapor pipe 88 and condensed in condenser 89, the distillate being collected in receiver 90 as a-product of the process. Clean gas oil reflux condensate collects in the base of the fractionator, is withdrawn by wayyof line SI and forced by pump 92 through heating coil 93 in furnace S5 and is therein raised to an active cracking temperature which may be somewhat less than that attained by the oil traversing coil 'Il but in excess of that to which the reduced crude and heavy gas oil condensate are raised in their respective heating coils. The cracked products so derived are conducted through transfer line 94 having control valve 95 into the base of evaporator '53,

Alternatively part or all of the reflux condensate from the base of fractionator S'I may be forced through pipe Sl and heating coil 'I of furnace 8 when this heating coil is not being used for heating fresh charging oil. In this heating coil the oil is raised to a cracking temperature such as that attained in the coil 93 and is then conducted through transfer line S8 having control valveVV 9g into the evaporator tower 73. InI this manner of operation the gas oil passes through the heating coil 'I by entering the convection section It@ of the coil and leavlng through the radiant section When this coil is used for preheating crude oil the flow is in the opposite direction, the crude oil entering the radiant section |0| and leaving through the convection section |00. Valves |02 and |03 are provided for controlling the flow of gas oil conducted from the tower 81 to the heating furnaces.

Cooling at the top of fractionator tower 81 is provided by withdrawing a side stream of reux condensate through line |04 and passing it through heat exchanger 4 and auxiliary cooler into the top of the tower, the necessary pres-- sure being provided by pump |06. Cooling for the top of fractionator section 43 of combination tower 4I is effected by pumping back to the top of the tower through pipe |01 under pressure generated by pump |03, a portion of the gasoline collected in receiver 49. Another por tion of this same gasoline distillate may be dig rected through connection |09 into the top of fuel oil flash tower 83, valves ||0 and furnishing the necessary control. Cooling for the top of crude iiash tower 3 is provided in a like manner, a portion of the gasoline collected in receiver I4 being forced through pipe ||2 and pump ||3 into the top of that tower, the necessary control being brought about through valve H4. Reflux condensate is withdrawn from trapout tray l l5 in tower 81 and directed by pressure of pump H1 through conduit H5 and heat ex changer 5 in indirect heat exchange relation with the crude oil charging stock, thence through auxiliary cooler ||9 and pipe 20 to an intermediate point in the tower 81. is provided to return a portion of this cooled reilux condensate to diiiierent levels in the evaporater tower 10 by way of valved pipes l 22 and |23. A by-pass control line |24 is arranged across the terminals of auxiliary cooling coil ||9 for control purposes. A connection |25 is furnished for leading oil to the base of the fractonator through valved pipe |26 and to the transfer lines 19 and 94 by way of valved terminal lines |21 and |28. Pump |29 gives the necessary pressure. By means of this line last-men tioned iluxing oil is injected into the transfer line to prevent coking difficulties. Surplus oil returns to fractionator 81 through the pipe |20.

Distillate collected in receiver 40 may be diverted from the process through draw-off line 5|, but preferably this distillate is passed through pipe 53|, heat exchanger 28, pipe |32, heat exchanger 01, and pipe |33, into an intermediate level in fractionator tower 81.

distillate may be directed to conduit for passage with the virgin stock through heating coil 11. In this case the distillate would desirably be mainly gasoline which it is desired to reform. Valved pipe |5| is provided to by-pass heat exchanger 28.

By returning distillate from the receiver i9 to either the fractionator 81 or the evaporator 10 or to both the fractionator 81 and evaporator 18, refractionation thereof takes place with the desirably light constituents passing oii overhead through vapor line 58 to be collected with the final desired gasoline distillate in receiver 90. Since refractionation takes place the end point of the distillate collected in receiver 0 need not be exactly that of the iinal desired product but it may be somewhat heavier including even light gas oil. In most instances it will be found desirable to pass the light gas oil into the re- Aline |2| i By-pass valve |88 is provided so that part or all of this ifi) ceiver 43 so that it can be introduced into the fractionator tower 01 and find its way through connection 9| to heating coil 03 for further cracking at fairly high cracking temperatures.

Reference numeral indicates a reduced pressure stripper tower into which an intermediate reflux condensate cut in the boiling range of light gas oil or furnace or tractor oil, for example, is directed by way of draw-oir line |35 which is connected to a trap-out tray |31 in the fractionator 81. This oil, after undergoing stripping in the tower |35, is withdrawn from the process as a, desired product, e. g., furnace oil, through valved draw-off line |33 while the over-head vapors from this stripper tower travel through pipe |39 into vapor line 45 for passage through condenser 48. A reuxing line for passing distillate from pipe |33 to the top of the stripper tower |35 is referred to by numeral |40.

In actual operation the temperature of the oil leaving the initial viscosity-breaking coil 36 is preferably in the neighborhood of BTW-900 F. and the pressure desirably being about 150-200 pounds per square inch. The temperature may, however, range from 850 to 950 F., more or less, and the pressure may be higher or lower than that indicated as preferable, extending, for example, from '15 pounds to 400 pounds per square inch, more or less. The heavy gas oil upon emerging from heating coil 55 preferably has a temperature of about 950 F., the pressure being desirably about 400 pounds per square inch. These values are preferred but the temperature may varyconsiderably ranging, for example, from 900 to 1000 F., and the pressure ranging from a few pounds per square inch to as high as 1000 pounds per square inch or more.

The mixture of virgin heavy naphtha and gas oil passing through the heating coil 11 is raised to a higher cracking temperature of, for example, about 1000 F1020 F. under a pressure of, for example, about '750 pounds per square inch although the temperature may range from 050 to 1150 F. and the pressure may also very considerably, for example from 200 pounds to i000 pounds per square inch. The reflux condensate from the base of fractionating column 31 is heated in. the coil 03 Aor in the coil 1, if that be used, under substantially the same conditions of temperature and pressure as mentioned for oil leaving coil 11, although a somewhat higher temperature and lower pressure may be used in some instances. The pressure maintained in the two evaporating zones 18 and 40 will depend upon the pressures used in the heating coils, necessarily being lower than the outlet pressure of any heating coil discharging thereinto. However, the pressure in evaporator 10 will be higher that held in evaporator section 40, the pressure in the former being, for example, about 2o0-300 pounds per square inch and that in the latter about pounds per square inch, more or less.

With this type of .operation a suitable boiling range for the kerosene fraction removed from the crude Hash tower and diverted from the process is about 450 to 550 F. This is merely illustrative as the boiling range may be somewhat higher or lower. The heavy naphtha and the gas oil which are mixed in accumulator lfor cracking together in coil 11 may have hoiling ranges of from 250 to 450 and 550 to 750 F., respectively, for example. The boiling range of the naphtha will depend upon the anti-i znook value desired for the nal gasoline distillate, the

higher the anti-knock value necessary the greater the quantity .of naphtha which must be reformed. and accordingly the lower the initial boiling point of the naphtha passed through coil Tl. The conversion to products in the gasoline boiling range per pass in the heating coils 3B, 55, 7l, and 93, may be about 10%, 15%, 60% and 20% respectively. But these values are merely illustrative and may be varied to suit dierent charging stocks and diierent desired products. Obviously the lighter and cleaner the stock the higher the rate of conversion may be. Referring to the coil 'Il high conversions per pass will follow from high initial gasoline content. Reaction chambers may be used with any or all of the cracking coils to provide for additional cracking.

In an alternative method of handling a crude oil charging stock, the crude charge introduced by pump 2, after preheating in heat exchangers,

such as 4 and 5, instead of being passed directly to the crude flash tower 3, is introduced into a pre-ilash drum for the release of light vapors which are passed into the lower part of the crude flash tower 3, and the residue from the pre-flash drum is passed through heating coil 'i and the heated crude directed through line E into the iiash tower 3.

While we have described a particular embodiment of our invention for purposes of illustration, it should be understood that various modications and adaptations thereof which will be obvious to one skilled in the art, may be made within the spirit of the invention as, set forth in the appended claims.

We claim:

l. The process of treating hydrocarbon oil which comprises raising heavy residual oil such as reduced `crude to a cracking temperature and subjecting it in a rst cracking Zone t0 viscositybreaking conditions to eiect conversion into gas oil constituents, separating the resulting cracked products into vapors and liquid residue in a separating zone, fractionating the vapors in a fractionating zone to form a heavy reflux condensate and a lighter fraction comprising gas oil constituents, raising heavy condensate so obtained to a cracking temperature and subjecting it in a second cracking zone to viscosity-breaking conditions to effect conversion into gas oil constituents. introducing the resulting cracked products into said separating zone, withdrawing liquid residue from said separating Zone and subjecting it to vacuum distillation in a flashing Zone held lunder sub-atmospheric pressure to form a heavy flash distillate, introducing flash distillate so obtained i into said fractionating zone so that any portion thereof remaining unvaporized after Contact with the vapors undergoing fractionation will be charged to said second cracking zone with said heavy reflux condensate, introducing said lighter fraction comprising gas oil constituents into a second fractionating zone wherein fractionation with the attendant formation of a nal desired light distillate and a reflux condensate occurs, heating reux condensate so obtained toa cracking temperature and subjecting it to conversion in a third cracking zone, separating resultant cracked products into vapors and liquid residue in a second separating zone, passing the separated vapors to said second fractionating zone, conducting the liquid residue with a reduction of pressure into a second hashing zone held at a higher pressure than said ashing zone rstmentioned, and mixing resulting vaporized fractions with the vapors liberated in said separating zone first-mentioned prior to the completion of the fractionation thereof.

2. The process of treatin-g hydrocarbon oil which comprises lightly cracking heavy residual cil such as reduced crude in a rst cracking Zone cy the application of heat, separating the cracked products into vapors and liquid residue in a rst separating zone, fractionating the vapors in a rlrst fractionating zone to form a light distillate and a heavy reilux condensate, withdrawing said liquid residue from the operation, cracking said heavy condensate by the application of heat in a second cracking zone, introducing the resulting cracked products into said first separating zone, introducing light distillate from the first fractionating zone into a second fractionating zone, for further fractionation, removfrorn said second fractionating zone fractionated vapors of the desired boiling characteristics and a reflux condensate, cracking said intermediate rei'lux condensate in a third cracking cone by the application of heat, separating the resulting cracked products into vapors and liquid residue in a second separating zone, conducting the vapors to said second fractionating Zone, passing the latter residue to a flashing zone with a reduction of pressure and introducing resulting vaporized fractions into said first fractionating zone.

3. A process in accordance with claim 2 wherein the heavy charging oil is reduced crude derived from a crude distillation operation, Wherein heavy naphtha, kerosene, and gas oil are likewise separated, said kerosene is Withdrawn from the process and said heavy naphtha and gas oil as a mixture are raised to a relatively high cracking temperature and subjected to conversion in a fourth cracking zone and the cracked products are introduced into said second separating zone.

4. in the cracking of hydrocarbon oils, the process that comprises subjecting heavy residual oil such as reduced crude to cracking temperature in a primary viscosity-breaking zone wherein the residual oil is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of gas oil constituents adapted for conversion into gasoline, directing the viscosity-broken products into a separating zone wherein separation of vapors from residue takes place, passing the separated vapors into a separate fractionating zone wherein the vapors are subjected to fractionation to forni a heavy reflux condensate and a lighter fraction comprising such gas oil constituents, passing said heavy reflux condensate to a .secondary viscositybreaking zone wherein the heavy condensate is subjected to cracking temperature under viscosity-loreaking conditions to effect the formation of a high yield of gas oil adapted for conversion into gasoline, separating the latter viscosity-hrokenv products into vapors and residue and passing the separated vapors into said separate fractionating zone, passing residual material separated out from the viscosity-broken products from both of said viscosity-breaking zones to a vacuum-dashing zone wherein the residual material is subjected to flash distillation under subatinospheric pressure to form heavy residue and vacuum-dashed distillate, introducing resultant vacuum-flashed distillate into the aforesaid fractionating zone so that any portion of the vacuurn-ilashed distillate remaining unvaporized after contact with the vapors undergoing fractionation therein will be charged to said secration of vapors from residue takes place and passing the separated vapors to a separate fractionating zone wherein the vapors are fractionated to recover a desired distillate product.

5. In the cracking of hydrocarbon oils, the process that comprises subjecting heavy residual oil such as reduced crude to cracking temperature in a primary viscosity-breaking zone wherein the residual oil is subjected to cracking temperature under viscosity-breaking conditions to eiect the formation of a high yield of gas oil constituents adapted for conversion into gasoline, directing the Viscosity-broken products into a separating zone wherein separation of vapors from residue takes place, passing the separated vapors into a fractionating zone wherein the vapors are subjected to fractionation to form a heavy reux condensate and a lighter fraction comprising gas oil constituents, passing said heavy reilux condensate to a secondary viscosity-breaking zone wherein the heavy condensate is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of gas oil constituents adapted for conversion into gasoline, separating the latter viscosity-broken products into vapors and residue and passing the separated vapors to the aforesaid fractionating zone for fractionation therein, introducing said lighter condensate comprising gas oil constituents into a second fractionating zone for fractionation therein so that gas oil constituents from the rst fractionating zone are combined with, and constitute a part of, a reflex condensate collected in the second fractionating zone, directing said reflux condensate to a separate cracking zone wherein the condensate is subjected to highcracking temperature under conditions of high cracking per pass to effect conversion into gasoline of high anti-knock quality, directing the resultant cracked products of the latter cracking into a separate separating zone wherein separation of vapors from residue takes place and passing the separated vapors to said second fractionating zone wherein the vapors are fractionated to separate out a gasoline distillate.

6. In the cracking of hydrocarbon oils the process that comprises primarily subjecting crude petroleum to a stripping operation to separate it into vapors and residue and fractionating the vapors in a iirst fractionating zone to form a condensate comprising gas oil constituents, passing said residue to a primary viscosity-breaking zone wherein the residue is subjected to cracking temperature under viscosity-breaking conditions to eiect the formation of a high yield of gas oil constituents adapted for conversion into gasoline, separating the viscosity-broken products into vapors and residue and passing the separated vapors into a second fractionating zone wherein the vapors are subjected to fractionation to form a heavy reflux condensate and a lighter fraction comprising gas oil constituents, passing resultant heavy renux condensate to a secondary viscosity-breaking zone wherein the heavy condensate is subjected to cracking temperature under viscosity-breaking conditions to ter viscosity-broken products into vapors and residue land passing the separated vapors into said second fractionating zone, passing said lighter condensate comprising gas oil constituents obtainedin the crude stripping operation to a separate cracking zonewherein the condensate is subjected to cracking temperature under conditions of high cracking per pass to effect conversion into gasoline of high anti-knock quality, separting the Aresultant cracked products of the latter cracking into vapors and residue and passing the separated vapors to a third fractionating zone wherein the vapors are fractionated to form a reiiux condensate and a nal distillate product, withdrawing said lighter fraction comprising gas cil constituents from the second fractionating zone and introducing it into the third fractionating zone whereby gas oil constituents of said lighter fraction are combined with, and constitute a part of, the reiux condensate collected in said third fractionating zone, passing the latter reflux condensate to a recycling cracking zone wherein it is subjected to cracking temperature to eiect conversion into gasoline constituents, separating the resultant cracked products formed in said recycling cracking zone into vapors and residue and passing the separated vapors into said third fractionating zone.

7. In the cracking of hydrocarbon oils the process that comprises primarily subjecting crude petroleum to a stripping operation to separate it into vapors and residue and fractionating the vapors in a rst fractionating zone to form a condensate comprising gas oil constituents, passing said residue to a primary viscositybreaking zone wherein the residue is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of gas oil constituents adapted for conversion into gasoline, separating the viscositybroken products into vapors and residue and passing the separated vapors into a second fractionating zone wherein the vapors are subjected to fractionation to separate heavy reux condensate from lighter gas oil constituents, passing resultant heavy reflux condensate .to a secondary viscosity-breaking zone wherein the heavy condensate is subjected to cracking ternperature under viscosity-breaking conditions to effect a high yield of gas oil constituents adapted for conversion into gasoline, separating the latter viscosity-broken products into vapors and residue and passing the separated vapors into said second fractionating zone, passing said .lighter condensate comprising gas oil constituents obtained in the crude stripping operation to `a single pass cracking zone wherein the condensate is subjected to cracking temperature under conditions of high cracking per pass to effect conversion into gasoline of high antiknock quality, separating the resultant cracked products of the latter cracking into vapors and residue and passing the separated vapors to a third fractionating zone wherein the vapors are fractionated to form a reux condensate and a final distillate product, combining lighter gas cil constituents from said second fractionating zone with reflux condensate formed in the third fractionating zone and passing the mixture to a recycling cracking zone wherein it is subjected to cracking temperature to effect conversion into gasoline constituents, separating the resultant cracked products formed in said recycling cracking zone into vapors and residue and passing the separated vapors into said third fractionating zone.

B'. In the cracking of hydrocarbon oils, the process that comprises subjecting heavy residual oil such as reduced crude to cracking tempera rture .in a primary viscosity-breaking zone wherein the residual oil is subjected to cracking temperature under viscosity-breaking conditions to effect the formation of a high yield of gas oil constituents adapted for conversion into gasoline, directing the viscosity-broken products into a separating Zone wherein separation of vapors from residue takes place, passing the separated vapors into a separate fractionating Zone wherein the vapors are subjected to fractionation to forni a heavy reflux condensate and a lighter fraction comprising such gas oil constituents, passing said heavy redux condensate to a secondary viscosity-breaking Zone wherein the heavy condensate is subjected to cracking temperature under viscosity-breaking conditions to efect the formation of a high yield of gas oil adapted for conversion into gasoline, separating the latter viscosity-broken products into vapors and residue and passing the separated vapors into said separate fractionating zone, passing residual material separated out from the viscosity-brokenv products from both of said viscosity-breaking zones to a vacuum-hashing zone wherein the residual material is subjected to flash distillation under subatniospheric pressure to form heavy residue and vacuurn-flashed distillate, introducing resultant vacuum-flashed distillate into the aforesaid fractionating zone so that any portion of the vacuum-flashed distillate remaining unvaporized after contact with the vapors undergoing fractionation therein will be charged to said secondary viscosity-breaking zone with said heavy reux condensate, introducing said lighter fraction comprising said gas oil constituents to a Second fractionating Zone for ractionating therein so that gas oil constituents from the rst fractionating zone are combined with, and constitute a part of, a reif flux condensate collected in the second fractionating zone, directing the latter reilux condensate to a separate cracking zone wherein the condensate is subjected to high cracking temperature under conditions of high cracking per pass to eiect conversion into gasoline of high anti-knock quality, directing the resultant cracked products of the latter cracking into a separate separating zone wherein separation of vapors from residue takes place and passing the separated vapors to said second fracticnating zone wherein the vapors are fractionated to separate out a gasoline distillate.

9. In the cracking of hydrocarbon oil the process that comprises primarily subjecting crude petroleum to a stripping operation to separate it into vapors and residue and fractionating the vapors in a iirst fractionating Zone to form a gas oil fraction, a kerosene fraction and a naphtha fraction, withdrawing said kerosene fraction as a product of the process, passing said residue to a primary viscosity-breaking zone wherein the residue is subjected to cracking temperature under conditions to eiect the formation of a high yield of gas oil constituents adapted for conversion into gasoline, separating the viscosity-broken products into vapors and residue and passing the separated vapors into a second ractionating zone wherein the vapors are subjected to fractionation to form a heavy reux condensate and a lighter fraction comprising gas oil constituents, passing resultant heavy reflux condensate to a secondary viscosity-breaking Zone wherein the heavy condensate is subjected to cracking temperature under conditions to effect a high yield of gas oil constituents adapted for conversion into gasoline, separating the latter viscosity-broken products into vapors and residue and passing the separated vapors into said second fractionating Zone, combining said naphtha and gas oil fractions obtained from said rst fractionating zone and passing the mixture to a separate cracking zone wherein the mixture is subjected to cracking temperature adequate to eiect reforming ci the naphtha constituents and maintained under conditions of high cracking per pass to effect conversion of gas oil constituents into gasoline of high anti-knock quality, separating the resultant cracked products of the latter cracking into vapors and residue, passing the separated vapors to a third fractionating Zone wherein the vapors are fractionated to form a reflux condensate and a distillate product, withdrawing said lighter fraction comprising gas oil constituents from said second fractionating zone and introducing it into said third iractionating zone whereby gas oil constituents of said lighter fraction are combined with, and constitute a part of, the reiiux condensate collected in the latter fractionating zone, passing the latter reiiux condensate to a cracking zone wherein it is subjected to cracking temperature to eiect conversion into gasoline constituents, separating the resultant cracked products formed in the latter cracking zone into vapors and residue and passing the separated vapors to said third fracticnating zone.

PERCIVAL C. KEITH, JR. JOSEPH K. ROBERTS.

CERTIFICATE vOF CORRECTION.

Patent No. 2,281,881. May 5, l9h2.

PERCIVAL C( KEITH, JR., ET AL.

It is hereby certified that .error appears in the printed specification of the above numbered patent requiring correction as follows: Page' LL, seo'- ond column,V line ZO-Zl, strike out "intermediate"; and that the said Letters Patent should be read with this correction therein that the same may conform to the 'record vof 'the oase in the Patent Office.

signed and Sealed this 25rd day of June, A. D.

Henry Van Arsdale, (Seal) Acting; Commissioner of Ph'thbs. 

